Multimedia server with simple adaptation to dynamic network loss conditions

ABSTRACT

A method for transmitting prioritized data encoded by a Forward Error Coding operation wherein a media object is separated into different classes of data forming a base layer and at least one enhancement layer of information, with each layer having associated parity data. Data of the separated media object, formed of classified data, is later encoded and stored, whereby information of the base layer is assigned a higher priority for transmission than enhancement layer data. Such priority classifications are used when a server transmits the classified data over a network fabric as prioritized data. Optionally, the composition of transmitted classified data is adjusted in view of a change in network conditions.

FIELD OF THE INVENTION

This invention relates towards the field of transmitting prioritizeddata based on network conditions.

BACKGROUND OF THE INVENTION

With the development of communications networks (network fabric) such asthe Internet and the wide acceptance of broadband connections, there isa demand by consumers for video and audio services (for example,television programs, movies, video conferencing, radio programming) thatcan be selected and delivered on demand through a communication network.Video services, referred to as media objects or streaming audio/video,often suffer from quality issues due to the bandwidth constraints andthe bursty nature of communications networks generally used forstreaming media delivery. The design of a streaming media deliverysystem therefore must consider codecs (encoder/decoder programs) usedfor delivering media objects, quality of service (QoS) issues inpresenting delivered media objects, and the transport of informationover communications networks used to deliver media objects, such asaudio and video data delivered in a signal.

Codecs are typically implemented through a combination of software andhardware. This system is used for encoding data representing a mediaobject at a transmission end of a communications network and fordecoding data at a receiver end of the communications network. Designconsiderations for codecs include such issues as bandwidth scalabilityover a network, computational complexity of encoding/decoding data,resilience to network losses (loss of data), and encoder/decoderlatencies for transmitting data representing media streams. Commonlyused codecs utilizing both Discrete Cosine Transformation (DCT) (e.g.,H.263+) and non-DCT techniques (e.g., wavelets and fractals) areexamples of codecs that consider these above detailed issues. Codecs arealso used to compress and decompress data because of the limitedbandwidth available through a communications network.

Quality of service issues relate to the delivery of audio and videoinformation and the overall experience for a user watching a mediastream. Media objects are delivered through a communications network,such as the Internet, in discrete units known as packets. These units ofinformation, typically transmitted in sequential order, are sent via theInternet through nodes commonly known as servers and routers. It istherefore possible that two sequentially transmitted packets arrive at adestination device at different times because the packets may takedifferent paths through the Internet. Consequentially, a QoS problemknown as dispersion could result where a packet transmitted later intime may be processed and displayed by a destination device before anearlier transmitted packet, leading to discontinuity of displayedevents. Similarly, it is possible for packets to be lost when beingtransmitted. A destination device typically performs an errorconcealment technique to hide the loss of data. Methods of ensuring QoSover a network such as over-allocating the number of transmitted packetsor improving quality of a network under a load state may be used, butthese methods introduce additional overhead requirements affectingcommunication network performance.

Communication networks control the transfer of data packets by the useof a schema known as a transport protocol. Transmission Control Protocol(TCP), described in Internet Engineering Task Force (IETF) Request ForComments (RFC) 793, is a well-known transport protocol that controls theflow of information throughout a communications network. A transportprotocol attempts to stabilize a communications network by maintainingparameters such as flow control, error control, and the time-organizeddelivery of data packets. These types of controls are administeredthrough the use of commands that exist in a header of a packet orseparately from packets transmitted between devices through thecommunications network. This control information works well for acommunications network that operates in a “synchronous” manner where thetransmission of data packets tends to be orderly.

Other types of media objects, in the form of streamed data, tend to bedelivered or generated asynchronous by where the flow of packets may notbe consistent. These packets are transmitted and received at differenttimes, hence asynchronously, where received packets are reconstituted inview of data in the headers of such packets. The transmission ofasynchronous packets suffers when network conditions drastically reducethe transmission (or receipt) of packets, resulting in network loss ofservice, degradation, or other conditions requiring a transmission totime out.

One way of reducing the amount of errors in the transmission of a datauses a technique called forward error coding (FEC) where some data isrepeated in a data stream. By using FEC, other methods of errorcorrection such as error concealment, flow control, and the like are notrequired for a user to acquire successfully a media object transmittedin a data stream. FEC however requires that the transmitter of datastream take into account network conditions that lead to a corruption orloss of data packets impacting an encoder that encodes data on the fly.

SUMMARY OF THE INVENTION

A method for transmitting prioritized data encoded by a Forward ErrorCoding operation is disclosed. A media object is separated intodifferent classes of data, forming a base layer and at least oneenhancement layer of information, with each layer having associatedparity data. Data of the separated media object, formed of classifieddata, is later encoded and stored, whereby information of the base layeris assigned a higher priority for transmission than enhancement layerdata. Such priority classifications are used when a server transmits acomposition of classified data over a network fabric, as prioritizeddata.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system illustrating the prioritization,encoding, and transmission of a media object, according to anillustrative embodiment of the invention.

FIG. 2 is a block diagram of a method for generating and transmittingclassified data representing a media object as prioritized data,according to an illustrative embodiment of the invention.

FIG. 3 is a block diagram of method decoding prioritized datarepresenting a media object, according to an illustrative embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, multimedia related data that is encoded and is latertransmitted represents a media object. The terms information and dataare also used synonymously throughout the text of the invention as todescribe pre or post encoded audio/video data. The term media objectincludes audio, video, textual, multimedia data files, and streamingmedia files. Multimedia files comprise any combination of text, image,video, and audio data. Streaming media comprises audio, video,multimedia, textual, and interactive data files that are delivered to auser's device via the Internet or other communications networkenvironment and begin to play on the user's computer/device beforedelivery of the entire file is completed. One advantage of streamingmedia is that streaming media files begin to play before the entire fileis downloaded, saving users the long wait typically associated withdownloading the entire file. Digitally recorded music, movies, trailers,news reports, radio broadcasts and live events have all contributed toan increase in streaming content on the Web. In addition, the reductionin cost of communications networks through the use of high-bandwidthconnections such as cable, DSL, T1 lines and wireless networks (e.g.,2.5 G or 3 G based cellular networks) are providing Internet users withspeedier access to streaming media content from news organizations,Hollywood studios, independent producers, record labels and even homeusers themselves.

The preferred embodiment of the invention makes use of a subset of FECtechniques known as forward erasure correction (FXC) where the contentof a media object is pre-encoded into separate partitions. Usingtechniques known in the art, a media object is encoded into differentclasses of data, referred to as classified data. Each class of datarepresents a different layer of information (i.e., a base andenhancement layers) where the base layer represents data crucial forrendering a media object and the enhancement layers being data that isless critical but important for adding detail to a rendered mediaobject.

The classified data is further refined by using systematic FXC codes,such as Reed Solomon (RS) codes, as to create parity data that istransmitted with the data representing base and enhancement layers of anencoded media object. Specifically, RS is used to produce erasure codesof various strengths whereby overhead rates for communication data canbe generated using a RS code with different (n, k) parameters; n equalto the total amount of data to be transmitted (encoded layer data withparity data) and k equal to the amount of encoded data.

When used for erasure correction, an RS code can correct up to h=n-kerasures (or the amount of data missing from a transmitted data stream).If the exemplary system uses a Galois Field with 8 bit symbols as thebasis of transmitted data, the maximum value of n is calculatedq=p{circumflex over ( )}r (q=maximum value of n, p=amount of datastates, r=number of items with data states). Hence, for an 8 bitsymbols, p=2 (a bit having two states) and r=8 (number of bits), themaximum value of n is 255.

Shorter length FXCs can be used by only computing and transmitting asmany parity bits that are as desired or needed. Once a maximum n iscalculated, a smaller RS(n′, k) may be derived from a RS(n, k) codewhere n′<n, which is modified depending on the desired erasureprotection strength (see, L. Rizzo, “Effective Erasure Codes forReliable Computer Communications Protocols”, Computer CommunicationReview, 27(2): pgs. 24-36, April 1997) The calculated parity bits forencoded data may change in accordance with network conditions or encoderperformance.

As an example of encoding a byte based code based on a 2{circumflex over( )}8 Galois Field, a maximum value of n=255 is calculated. A RS(n′,k)code is selected, where the Reed Solomon code is based on an RS(255, k),and n′-k parity bytes are encoded. As the value of n′ increases, theoriginal parity bytes encoded (n′-k) are not changed. That is, for aReed Solomon code for a RS(11, 10) based on a RS(255, 10), the 11thparity byte has the same value as the 11th parity byte in an RS(12, 10)code. It is to be noted that the principles of the present invention maybe modified to accommodate different values of n, n′, p, r, and kdepending on the needs of an encoding/transmitting system.

Preferably, RS coding of data is interleaved across packets or frames.That is, entire packets or frames will be made up of either informationor parity data. These packets, in order to simplify the process ofidentifying missing packets, may be identified by information in thepacket headers. Hence, a media object requester would be able toidentify missing packets if the packet headers are sequentiallygenerated, and there is a gap in the numeric sequence. Real TimeTransport Protocol (RTP) is one transport mechanism used for generatingsequential packet headers, although other transport protocols may beselected in accordance with the principles of the present invention.

Additionally, different levels of channel loss protection are achievedby grouping parity packets into several multicast groups. A clientreceiving such data can adjust the level of channel loss protection byjoining (or leaving) as many multicast groups as needed, hence theclient may adapt to the loss of data by increasing the channel bandwidthby joining more multicast groups, as needed. This technique ofmulticasting is described because the source-encoding rate of a FXCencoder is typically is not adjusted in the case where content ispre-encoded and stored on a storage device, for an exemplary embodimentof the present invention.

When encoding a media object separated into different classes of datalayers, it is desirable to offer a higher FXC strength for base layerdata and a lower FXC strength for enhancement layer data is accomplishedby using scalable video compression with unequal error protection. Foran exemplary embodiment of the present invention, a media object isseparated into two layers of classified data: base layer information(Bi) and enhancement layer information (Ei). Accordingly, the base layerhas parity data (Bp) and the enhancement layer has parity data (Ep);each of layer and parity data are afforded their own data types. Bi andBp is data that is more important than Ei and Ep data, because Bi and Bpdata is more critical for rendering media object than Ei and Ep data. Itshould be noted that the principles of the present invention apply wherea media object is prioritized into as many layers as needed, forexample, one base layer and multiple enhancement layers.

An exemplary embodiment of the invention, shown as encoding system 100in FIG. 1, presents scalable video encoder 110 that creates compressedbit streams from a media object being encoded. Scalable video encoder110 may be implemented in software, hardware, or in a combination ofboth. The media object is divided into separate layers of classifieddata as described above, where the data once separated, is placed in abitstream corresponding to a priority assigned to each layer and packedinto packets for network transmission via network fabric 160, such as acommunications network or the Internet. Preferably, each layer is FXCencoded, using a systematic FEC encoder 115, 120 across packets forprotection against network packet loss. The priority of each layer ofclassified data is associated with the importance of transmitted dataeventually used to render a media object.

More specifically in this exemplary embodiment, scalable video encoder110 separates the media object into two layers, representing a baselayer and an enhancement layer. Data representing the base layer isinputted into FEC encoder 115 where Bi information is generated via aFXC encoding process. This generated data is stored as pre-encoded datain Bi storage 125. FEC encoder 115 also creates Bp data that is storedin Bp storage 130 when generating Bi information.

Similarly, data representing the enhancement layer is inputted into FECencoder 120 where Ei information is generated via a FXC encodingprocess. This generated data is stored as pre-encoded data in Ei storage135. FEC encoder 115 also creates Ep data that is stored in Ep storage140 when generating Ei information. Different strength FXC codes can beused for the base and enhancement layers, depending on network andsystem requirements. Preferably, when adjusting the FXC strength oftransmitted RS codes, an indication the contents of data packets istransmitted, either in data packet headers or as separate sideinformation.

When a request is made for a media object via network fabric 160,multimedia server 150 preferably determines the available bandwidth andexpected (or real time) network loss conditions that effect therequester of the media object. This type of determination may be madebased on a user profile, information communicated in the request for amedia object, historical network conditions, network service reportinginformation (such as Real time Transport Control Protocol (RTCP) reportsobtained during the transmission of data), and the like. Optionally,multimedia server 150 determines the type of network path to be used todeliver the pre-encoded media object to estimate a possible networkloss. For example, multimedia server 150 expects a higher loss rate ofdata when a wireless connection is used versus a landline or broadbandconnection to communicate data.

Multimedia server 150, in response to the determination of networkconditions, selects Bi, Bp, Ei, and Ep data from their associatedstorage areas based on the level of priority assigned to the selecteddata. This priority level is related to the importance of the data asused to render a media object. Hence, base layer data is considered moreimportant and is more likely to be transmitted than enhancement layerdata during periods of network congestion. After selecting classes ofdata to be transmitted, multimedia server 150 creates a composition ofclassified data by prioritizing and formatting such selected data. Thiscomposition of classified data, known as prioritized data, reflectsmultimedia encoder 150 adjusting the classes of data transmitted in viewof network conditions, where a minimum level of base layer informationis required to render a media object. As network conditions improve, thecomposition of classified data includes more enhancement layerinformation and associated parity information.

Multimedia server 150 transmits data packets of prioritized data overnetwork fabric 160. Specifically, multimedia server 150 seeks tooptimize the playback quality of multimedia data received by a requestorof a media object by adjusting the composition of Bi, Bp, Ei, and Eptransmitted in accordance with their respective priorityclassifications. For example, if no loss of data is expected from anetwork, multimedia server transmits all of the Bi and Ei information indata packets. Bp and Ep data is transmitted as space/bandwidth allows,preferably with more Bp data being transmitted than Ep data.

When there is an expected level of network loss, multimedia server 150replaces Ep data with Bp data in the composition forming prioritizeddata. With very high levels of expected network loss, multimedia serverreplaces an amount of Ei information transmitted with Bp data because arequested media object will not be capable of being rendered without abaseline of Bi information that is received or recovered using Bp data.It is to be noted that there may be a limit to the bandwidth availableto a media object requester due to physical or pre-set bandwidth limitsof a network.

In an optional embodiment of the present invention, multimedia server150 attempts to optimize the delivery of a media object to a requestorby determining the amount of expected network loss, as explained above.Assuming that the bandwidth to a requestor is fixed, multimedia server150 transmits a composition of Bi information and an amount of Bp datanecessary to achieve a corrected error rate, in response to the expectednetwork loss. If there is any available bandwidth after the transmissionof Bi and Bp data, multimedia server 150 fills the space first with Eiand then Ep data. The tradeoff between transmitting Bp versus Ei or Epdepends on many factors such as the expected range of network lossconditions, effectiveness of the scalable encoding, viewer preferences,nodes in a network, and the like.

Preferably, multimedia server 150 will use high strength FXC codes whentransmitting Bi, Bp, Ei, and Ep data representing an encoded mediaobject. By using system 100, stored FXC codes will not need to berecomputed each time expected network conditions change for a new mediaobject requestor.

In the operation of encoding system 100, a temporal encoding techniqueis preferred over spatial, Signal Noise Ratio (SNR), or simple datapartitioning encoding techniques because temporal based processes do notsuffer from the problem of “drift”. Specifically, when decoding an mediaobject that has been prioritized and separated into layers, periods ofdrift occur when decoding base and enhancement layer data afterexclusively decoding base layer data. The reconstructed media object(especially video) rendered from the base and enhancement layer datawill continue to appear as if it were being rendered during the time ofjust base layer data. This drift effect is minimized if base andenhancement layers were exclusively used for decoding a media object.

The problem of drift is eliminated when temporally encoded video basedmedia objects place bidirectional “B” coded pictures in the enhancementlayer, and “I” and “P” frames are placed in the base layer. Preferably,the B coded pictures in the enhancement layer are not used to predictother pictures. Hence, when media server 150 transmits Bp data insteadof Ei information, a media object requestor's video frame rate isreduced, but the per frame video quality is not reduced if the FXC codestrength is sufficient to correct all network loss.

During periods of network disruption, a media object requestor would usecorrectly received Ei information to increase the frame rate of video,which is be greater than the frame rate of video using only base layerdata. When network conditions improve, more Ei information istransmitted, and the frame rate of the video will likewise improve, withthe quality of rendered video. Optionally, the media object requester(or decoder of the media object requestor) may request that thecomposition of transmitted Bi, Bp, Ei, and Ep data as priority data bechanged in accordance with network conditions. Multimedia server 150implements this request.

Ideally, Bi, Bp, Ei, and Ep data are packed into data packets, wherefixed sizes of data packets are used. Multimedia server 150 is able toswap entire data packets during transmission, as to maintain a constantdata transmission rate. A drawback to this technique however prevents acorrespondence between video frames or slices and data packets, assuggested in IETF RFC 2250 and RFC 2190. An alternative embodiment ofthe present invention is supported where the data packets do correspondto video frames or slices, which depends upon the technique selected forpacking and processing data packets.

FIG. 2 represents block diagram of a method 200 for the transmission ofprioritized data representing a media object by multimedia server 150,in accordance with an exemplary embodiment of the present invention. Instep 210, scalable video encoder 110 and FEC encoders 115 and 120 encodea media object into levels of classified data. Specifically, scalableencoder 110 separates a media object into several classes of data,denoted as separate layers, with each layer corresponding to theimportance of data used for rendering a media object. The layers of dataform a base layer and at least one enhancement layer(s) of information.The separated layers of classified data are relayed to FEC encoders 115and 120 for FXC encoding. During the encoding process, parity dataassociated to each layer is generated and is later stored in step 220.Importantly, the generated information and parity data corresponding toeach layer is stored in their respective storage areas, such as baselayer information being stored in Bi storage 125 and the associatedpriority information being stored in Bp storage 130. Optionally, thereare as many storage areas as there are layers of classified data.

Multimedia server 150, in response to a request for a media object,prioritizes a composition of classified data into prioritized data andtransmits such data in response to network conditions in step 230. Theprioritization of classified data is determined by the level of priorityassigned to each layer of classified data. Multimedia server 150 formsthe composition of classified data, as prioritized data, in view ofnetwork conditions. When network conditions result in the loss of data,data with a higher priority level is more likely to be transmitted thandata with a lower priority level. Conversely, data with a lower priorityis more likely to be transmitted when network conditions result in fewerdata packets being loss.

The determination of network conditions, as described above, may eitherbe expected or real-time network conditions. Accordingly, multimediaserver 150 retrieves data from storage 125, 130, 135, and 140 inaccordance with network conditions. If a network encounters manyproblems, more Bi, and Bp data is retrieved and transmitted over networkfabric 160, versus periods of no network problems where more Ei and Epdata is transmitted.

Multimedia server 150 adjusts the composition of classified data,forming prioritized data, in response to a change in network conditionsin step 240. If network conditions improve, multimedia server 150 willtransmit more enhancement layer related information (Ei, Ep). If networkconditions worsen during a transmission, multimedia server 150 willreplace enhancement layer associated data with more base layerassociated data (Bi, Bp). This process may be repeated between steps 230and 240 as network conditions change frequently.

FIG. 3 presents a block diagram of method 300 for an exemplaryembodiment of a decoder decoding prioritized data operating inaccordance with the principles of the present invention. Specially, instep 310 a media object requester makes a request for a media object vianetwork fabric 160. Multimedia server 150 preferably receives thisrequest, where the present network conditions of the requester arecommunicated with the request.

In step 320, a decoder used by the media object requester begins toprocess received prioritized data, wherein such data preferably has atleast Bi information. The decoder uses prioritized data formed of acomposition of classified data to render a media object as audio, video,or a combination of both. If the decoder receives more Ei data, adecoder renders a media object at a higher level of quality thanpossible with just Bi information. The receipt of parity data related toeither the base layer or enhancement layer(s) assists in the generationof missing Bi or Ei information if network conditions result in the lossof transmitted data.

In an optional embodiment of the invention, a decoder uses FXC decodingif data was lost during the receipt of data packets representing a mediaobject. Specifically, the decoder may not receive all of the transmitteddata representing either Bi or Ei information. By using FXC decoding,the decoder generates missing Bi information from received Bp data andmissing Ei information from received Ep data.

The decoder, in step 330, requests that the composition of classifieddata transmitted as prioritized data change, because network conditionsare different. Specifically, the decoder either requests thatenhancement layer information be replaced by base layer parity data, fordegrading network conditions, or for more enhancement layer or paritydata for improving network conditions. The mechanics of the decoder ofthe media object requestor is similar to the inverse of the operation ofscalable video encoder 110.

The present invention may be embodied in the form ofcomputer-implemented processes and apparatus for practicing thoseprocesses. The present invention may also be embodied in the form ofcomputer program code embodied in tangible media, such as floppydiskettes, read only memories (ROMs), CD-ROMs, hard drives, high densitydisk, or any other computer-readable storage medium, wherein, when thecomputer program code is loaded into and executed by a computer, thecomputer becomes an apparatus for practicing the invention. The presentinvention may also be embodied in the form of computer program code, forexample, whether stored in a storage medium, loaded into and/or executedby a computer, or transmitted over some transmission medium, such asover electrical wiring or cabling, through fiber optics, or viaelectromagnetic radiation, wherein, when the computer program code isloaded into and executed by a computer, the computer becomes anapparatus for practicing the invention. When implemented on ageneral-purpose processor, the computer program code segments configurethe processor to create specific logic circuits.

1. A method for communicating data representing a media object encodedinto classified data representing base layer information and enhancementlayer information through a network fabric comprising the steps of:transmitting a composition of the classified data as prioritized data inresponse to network conditions wherein the classified data comprises atleast one of base layer information with associated parity information;adjusting a composition of prioritized data for transmission in responseto a change in network conditions wherein the composition of classifieddata is modified with enhancement layer information.
 2. The method ofclaim 1, wherein the classified data is pre-encoded.
 3. The method ofclaim 1, wherein the transmitting step is enabled by a multimediaserver.
 4. The method of claim 1, wherein the prioritized data isencoded by an encoding operation selected from at least one of: temporalscalability and data partitioning.
 5. The method of claim 1, wherein theprioritized data is transmitted as data packets that are sequentiallynumbered.
 6. The method of claim 1, wherein the adjusting step reducesan amount of the enhancement layer information and increases an amountof the base layer parity data forming the composition of priority datawhen network conditions degrade rendering the media object.
 7. Themethod of claim 1, wherein the adjusting step reduces an amount of thebase layer information and associated parity information and increasesan amount of the enhancement layer information and associated paritydata forming the composition of priority data when network conditionsare favorable for rendering the media object.
 8. The method of claim 1,wherein the classified data is pre-encoded by a forward error correctioncode operation using Reed Solomon codes and the classified data isstored according to data class.
 9. The method of claim 8, wherein amultimedia server selects the composition of prioritized data to betransmitted based on network conditions by accessing a data storecorresponding to data class.
 10. The method of claim 1, wherein morethan one layer of enhancement information and associated priority dataform the classified data.
 11. The method of claim 1, wherein networkconditions considered during the transmission step comprise as least oneof: available bandwidth, expected loss of transmitted data, actual lossof transmitted data based on a user profile, historic networkconditions, and a specific request for the composition of classifieddata transmitted as the prioritized data.
 12. The method of claim 1,wherein network conditions considered during the adjustment stepcomprise at least one of: a change in available bandwidth, a change inthe expected loss of transmitted data, a change in the loss oftransmitted data, and a request to change the composition of classifieddata transmitted as the prioritized data.
 13. A method for communicatingdata representing a media object comprising the steps of: determiningnetwork conditions: transmitting prioritized data in accordance withnetwork conditions, wherein the prioritized data is generated as acomposition of classified data representing at least one base layer ofinformation and at least one enhancement layer of information withparity data being associated with each layer of information; and thecomposition of transmitted base layer information with associated paritydata and the enhancement layer information with associated parity datais determined in response to network conditions.
 14. The method of claim13, wherein more base layer parity data is transmitted in thecomposition of classified data when network conditions result in a lossof data.
 15. The method of claim 13, wherein more enhancement layerinformation is transmitted in the composition of classified data whennetwork conditions result in more data being successfully received. 16.The method of claim 13, wherein prioritized data is sent in the form ofdata packets.
 17. The method of claim 16, wherein data packets arepacked with more enhancement layer information with associated paritydata when space is available.
 18. The method of claim 13, wherein thecomposition of classified data transmitted as the prioritized data ischanged in response to a request from a decoder.
 19. The method of claim13, wherein network conditions considered during the determination stepcomprise as least one of: available bandwidth, expected loss oftransmitted data, actual loss of transmitted data based on a userprofile, historic network conditions, and a specific request for thecomposition of classified data transmitted as the prioritized data. 20.A method for decoding communicated data representing a media objectcomprising the steps of: processing prioritized data, wherein theprioritized data represents a composition of classified data that ispre-encoded into at least one base layer of information and at least oneenhancement layer of information with parity data being associated witheach layer of information; and requesting that the composition ofclassified data transmitted as prioritized data change to reflectdifferent network conditions.
 21. The method of claim 20, wherein theprocessing step uses Forward Erasure Correction (FXC) for generatingmissing layer information from the parity data associated with the layermissing such information.